Method for adapting a torque converter lock-up clutch

ABSTRACT

For a torque converter lock-up clutch ( 7 ) a method is proposed in which an application pressure is adapted. To this end, within a first interval, a pressure change is output after a transition function and the existence of the reaction of the torque converter lock-up clutch is tested after output of the application pressure during an application phase from an electronic gear control ( 13 ). In the absence of reaction, additional intervals are then output. The application phase is then terminated when the reaction of the torque converter lock-up clutch occurs. The control/regulating phase for the torque converter lock-up clutch ( 7 ) follows after the application phase terminates.

BACKGROUND OF THE INVENTION

The invention relates to a method for adapting a torque converterlock-up clutch in an automatic transmission where an electronic gearcontrol outputs an application pressure upon detecting the need of achange of state of the torque converter lock-up clutch. From revertivevariables, the electronic gear control detects a change of state of thetorque converter lock-up clutch during a control/regulating phase. Theelectronic gear control then determines therefrom an adaptation valuefor the application pressure.

In torque converter lock-up clutches, the problem arises in the practicethat the application behavior thereof clearly depends on the mechanicalaxial play of the system, the so-called release play. A differentrelease play causes a different operating comfort during state changesof the torque converter lock-up clutch, such as from open to regulatedor from open to closed. DE-OS 41 11 081 proposes as solution for thisthat during a controlled/regulated transition from open to closed theapplication pressure be tested by measuring the change of the slipwithin a preset period of time. The application pressure is thenadequately adapted according to the time period measured.

Based on the above described prior art, the problem to be solved by theinvention is further to develop the prior art.

SUMMARY OF THE INVENTION

According to the invention, the problem is solved in that after outputof the application pressure an application phase for the torqueconverter lock-up clutch follows wherein, during the application phase,the electronic gear control outputs, within a first interval, a pressurechange after a transition function and tests the existence of thereaction of the torque converter lock-up clutch. In the absence ofreaction, the electronic gear control then outputs further intervals.The application phase ends when a reaction of the torque converterlock-up clutch occurs, the electronic gear control then continuing withthe control/regulating phase. According to claim 2, the reaction of thetorque converter lock-up clutch may be detected when a differentialrotational speed calculated from pump and turbine rotational speedsfalls below a limit value. The inventive solution offers the advantageof it being possible to enlarge the tolerances within the limits ofwhich must lie the produced hydrodynamic torque converters, includingthe torque converter lock-up clutch. This results in a correspondinglowering of cost.

In a development of the invention, it is proposed that the newapplication pressure be calculated by weighting, with a factor, thepressure value existing during occurrence of the reaction of the torqueconverter lock-up clutch.

In one other development of the invention, it is proposed that as anadditional safety function the intervals output during the applicationphase is added up and an error is entered in a diagnosis system when theaddition exceeds a limit value. As consequent reaction, it is thenpossible, as proposed in claim 5, to activate a substitute program bymeans of which the preset state changes of the torque converter lock-upclutch, e.g. the regulated operation, is no longer permitted.

In another development, it is proposed that with the beginning of themethod for adapting the torque converter lock-up clutch, a time step isstarted and a renewed method for adaptation be applied only when thetime step exceeds a limit value. Therefore, it is hereby taken intoconsideration that the changes of the torque converter lock-up clutch,such as friction value change, occur slowly. It is thus enough, when theadaptation method is operated with long periods of time. Thus, thereresults altogether the advantage of a quicker program sequence.

BRIEF DESCRIPTION OF THE DRAWING

The drawings show a preferred embodiment wherein:

FIG. 1 is a system diagram;

FIG. 2 is a program sequence plan; and

FIGS. 3A and 3B a time diagram.

DESCRIPTION OF THE PREFERRED EMBODIMENT

FIG. 1 shows a system diagram of an automatic transmission. It consistsof the mechanical part proper, a hydrodynamic torque converter 3, ahydraulic control unit 21 and an electronic gear control 13. Theautomatic transmission is driven by a drive unit 1, preferably aninternal combustion engine, via an input shaft 2. The latter isnon-rotatably connected with the impeller 4 of the hydrodynamic torqueconverter 3. As known per se, the hydrodynamic torque converter 3consists of an impeller 4, a turbine wheel 5 and a stator 6. A torqueconverter lock-up clutch 7 is situated parallel with the hydrodynamictorque converter 3. The torque converter lock-up clutch 7 and theturbine wheel 5 lead to a turbine shaft 8. When the converter lock-upclutch 7 is actuated, the turbine shaft 8 has the same rotational speedas the input shaft 2. The mechanical part of the automatic transmissionconsists of clutches and brakes A to G, a free wheel 10 (FL1), aRavigneaux set 9 and a rear-mounted planetary gear set 11. The outputtakes place via a transmission output shaft 12. The latter leads to adifferential (not shown), which drives the output of a vehicle (notshown), via two axle half shafts. A gear step is established by aclutch-brake combination. Since the mechanical part is not relevant forfurther understanding of the invention, a detailed description isomitted.

Depending on the input variables 18 to 20, the electronic gear control13 selects a drive step. Via the hydraulic control unit 21, whereelectromagnetic actuators are located, the electronic gear control 13then activates a clutch/brake combination and controls/regulates thestate of the torque converter lock-up clutch. During the shifttransitions, the electronic gear control 13 determines the pressurecurve of the clutches/brakes taking part in the gear shift. In theelectronic gear control 13, there are shown as blocks in simplifiedform: micro-controller 14, memory 15, function block control actuators16 and function block calculation 17. In the memory 15 are stored thedata relevant to the transmission. Data relevant to the transmissionare, e.g. programs and specific characteristic values of the vehicle,adaptation values and diagnosis data and shift characteristic fields.The memory 15 is usually designed as EPROM, EEPROM or buffered RAM. Inthe function block calculation 17 are calculated the data relevant for ashift curve. The function block control actuators 16 serves for controlof the actuators located in the hydraulic control unit 21. Inputvariables 20 are fed to the electronic gear control 13. Input variablesare, e.g. a variable representative of the driver's desired performance,such as the accelerator pedal/throttle valve position or manual gearshift requirements, the signal of the torque generated by the internalcombustion engine, the rotational speed and temperature of the internalcombustion engine, etc. The specific data of the internal combustionengine are provided by an engine control unit 22, via data line 23. Asadditional input variables the electronic gear control 13 receives therotational speed of the turbine wheel 18 and of the transmission outputshaft 19.

In FIG. 2 is shown a program flow chart for the adaptation method of thetorque converter lock-up clutch. This starts at step S1 with the inquiryof whether the marginal conditions have been satisfied. These aresatisfied when:

the transmission oil temperature theta (ATF) is higher than a limitvalue and

coasting operation has been detected and

the rotational speed of the input unit nMOT is higher than a limitvalue.

If the marginal conditions have not been satisfied, the programterminates. In case of positive inquiry, it is then tested in step S2whether a time step tADA is greater than a limit value. The time steptADA is started after a first adaptation value has been determined. Thistime step causes a new adaptation be carried out, only after lapse ofsaid time step, e.g. 40 hours. Thereby is taken into account thecircumstance in which an operation of the torque converter lock-upclutch occurs only very slowly. In case of negative inquiry, i.e. thetime step tADA still has not lapsed, the program terminates. In case ofpositive inquiry result in step S2, an application pressure p0 is outputin step S2. In step S4, a counting variable i is preset. In step S5, theelectronic gear control 13 then outputs a transition function in theinterval T(i). The transition function is shown in FIG. 3B.

Thereafter in step S6 follows a calculation of the rotational speeddifference dn from the pump rotational speed nP minus the turbinerotational speed nT. In step S7, it is tested whether the rotationalspeed difference is higher than a limit value. If this is not the case,i.e. still no reaction of the torque converter lock-up clutch can bemeasured, in step S8 is inquired whether the counting variable i hasreached a maximum value iMAX. This is the case when the electronic gearcontrol has output a preset number of intervals T(i) without a reactionof the torque converter lock-up clutch having been detected. In thiscase, an error entry in the diagnosis and the activation of a substituteprogram follow in step S12. The effect of this is that the preset statechanges of the torque converter lock-up clutch, such as the regulatedoperation, are no longer admitted. Thereafter the program sequenceterminates.

If the counting variable i still has not reached the maximum value, thevariable is increased by one in step S9 and the loop is continued withstep S5 with the renewed output of the transition function in theinterval T(i+1). In step S7, if it is established that a reaction of thetorque converter lock-up clutch exists, i.e. the rotational speeddifference dn is more than the limit value GW, then in step S10 the newapplication pressure p0(NEU) is calculated by weighing the pressurelevel at which the reaction of the torque converter lock-up clutchappeared, p(REA) with one factor. In the practice, it is obviouslypossible to use, instead of the pressure p(REA), the current valueoutput by the electronic gear control to the electromagnetic actuator.Thereafter the new application pressure p0(NEU) is stored in step S11 asan actual application pressure. Thereafter the program flow chartterminates.

FIG. 3 comprises two parts, FIGS. 3A and 3B. Here each one shows in thecourse of time:

FIG. 3A the curve of the rotational speed difference dn calculated formthe pump rotational speed nP minus the turbine rotational speed nT; and

FIG. 3B the transition function for the pressure level of the torqueconverter lock-up clutch output by the electronic gear control duringseveral intervals T(i).

The first interval T(1) starts at the t0 moment. This lasts up to the t2moment. For the time period t0 to t1, the pressure level is increasedlinearly from the initial value p0 up to the value p1. For the timespace t1 to t2, the pressure level remains constant. The transitionfunction thus corresponds to the pressure curve p0 after p1 and afterp2. During the time space t2 to t3, the electronic gear control testswhether a rotational speed difference dn appears. Since this is not thecase, at the t3 moment the second interval T(2) begins. This lasts up tothe time space t4. During the second interval T(2), the same transitionfunction is output from the curve. Compared with the first intervalT(1), the pressure level, however, is increased specifically to thepressure level p2. The test at the end of the second interval T(2), i.e.the t4 moment, results in that the rotational speed difference dn stillhas not changed. Thus at the t5 moment, the electronic gear controloutputs a third interval. At the t6 moment, the rotational speeddifference dn begins to change in point B. At the t7 moment, therotational speed difference dn has fallen below a limit value GW in thepoint C. This is the case when the torque converter lock-up clutch isclose. Thereafter the control/regulating phase for the torque converterlock-up clutch begins in point A. The pressure level in point A, whichcorresponds to p(REA) from FIG. 2, is weighed with a factor F. For thesubsequent gear shifts of the torque converter lock-up clutch, a newapplication pressure p0 is thus output according to p0 =p(REA) x F.

Reference numerals

1 drive unit

2 input shaft

3 hydrodynamic torque converter

4 impeller

5 turbine wheel

6 stator

7 torque converter lock-up clutch

8 turbine shaft

9 ravigneaux set

10 free wheel fL1

11 planetary gear set

12 transmission output shaft

13 electronic transmission control

14 micro-controller

15 memory

16 function block control actuators

17 function block calculation

18 turbine rotational speed signal

19 transmission output rotational speed signal

20 input variables

21 hydraulic control unit

22 electronic engine control

23 data line

What is claimed is:
 1. A method of adaptation of a torque converterlock-up clutch (7) of an automatic transmission comprising a) upondetection of the requirement of a change of state of said torqueconverter lock-up clutch an electronic gear control (13) outputs anapplication pressure (p0), during a control/regulating phase of a statechange of said torque converter lock-up clutch (7), b) said electronicgear control (13) detects, from revertive variables, a reaction of saidtorque converter lock-up clutch (7) and therefrom determines anadaptation value for the application pressure (p0), c) after output ofthe application pressure (p0) there follows an application phase forsaid torque converter lock-up clutch (7), wherein d) during theapplication phase said electronic gear control (13) outputs, within afirst interval (T(1)), a pressure change after a transition function andtests the existence of the reaction of said torque converter lock-upclutch (7), e) in the absence of reaction outputs additional intervals(T(i), i =2, 3, . . . n) wherein said electronic gear control (13)within said additional intervals (T(i), i =2, 3, . . . , n) outputs apressure change based on the pressure at the end of the previousinternal (T(i−1), i +2, 3, . . . , n) after the same transition functionand f) the application phase terminates when a reaction of said torqueconverter clutch (7) occurs; said electronic gear control (13)thereafter continuing with the control/regulating phase.
 2. The methodaccording to claim 1, wherein the occurrence of the reaction of saidtorque converter lock-up clutch (7) is detected when a rotational speeddifference (dn) calculated from pump (nP) and turbine (nT) rotationalspeeds falls below (dn<GW) a limit value (GW).
 3. The method accordingto claim 2, wherein a new application pressure (p0(NEU)) is calculatedby weighing a pressure value (p(REA)) existing when the reaction of saidtorque converter lock-up clutch (7) appears with a factor (F)(p0(NEU)=F·p(REA)).
 4. The method according to claim 3, whereinintervals output during the application phase are added up (SUM(T(i)))and an error is entered in a diagnosis system (17) when the sum(SUM(T(i))) exceeds a limit value (SUM(T(i)))>GW).
 5. The methodaccording to claim 4, wherein, with the error entry, a substitutionprogram is actuated by means of which preset state changes of saidtorque converter lock-up clutch (7) are no longer permitted.
 6. Themethod according to claim 1, wherein with the beginning of the methodfor adaptation of said torque converter lock-up clutch, a time step(tADA) is started and a renewed method for adaptation is applied onlywhen the time step (tADA) exceeds a limit value (GW).
 7. The methodaccording to claim 4, wherein the method for adaptation is applied onlywhen the following conditions are satisfied: i) the transmission oiltemperature (theta(ATF)) is higher than a limit value (theta(ATF)>GW);ii) coasting operation is detected; and iii) rotational speed of theinternal combustion engine (nMOT) is higher than a limit value(nMOT>GW).